1. Field
The described technology relates generally to a foldable display device.
2. Description of the Related Art
Examples of currently popular flat panel displays include a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting device (OLED), an electric field effect display (FED), and an electrophoretic display (EPD).
In a display device, generally, layers such as a display panel including a thin film transistor and an emission layer, a polarization film on the display panel, and a touch screen panel (TSP) are laminated. At the outermost portion of the display device, the layers, such as the display panel, the polarization film, and the touch screen panel, are encapsulated by using a transparent window to prevent moisture or oxygen from penetrating from the outside.
Particularly, in the case of a foldable display device, a flexible display panel is utilized, and each of the layers is adhered by a pressure sensitive adhesive (PSA), and each layer has a natural folding shape due to a tensile limitation of a material thereof. Also, when being assembled to the display device having a set shape, the natural folding shape must be forced to fit the set shape.
As shown in FIG. 7 and FIG. 8, after mounting a display module 2, which includes a window layer 2-1 adhered to a display panel 2-3 and a lower film 2-4 by an adhesive 2-2, to a folding evaluation jig 1, when folding the display module 2 with respect to a rotation axis of the jig 1, an actual tensile stress that is applied to the window layer 2-1 is less than a required tensile stress, and an actual compression stress that is applied to the lower film 2-4 is greater than a required compression stress. As such, the compression stress that is applied to the side of the lower film 2-4 increases, and the lower film 2-4 adhered by the adhesive 2-2 receives a large degree of the compression stress, such that the layer of interlayer adhesion may fail and cause separation, such that a defect such as buckling or peeling is generated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art.